1. Field of the Invention
The present invention relates to a hydraulic (actuation) system applied to wind turbine blade pitch control or the like and adapted to supply oil from a hydraulic tank into a hydraulic unit for blade pitch control (hydraulic actuation system such as a hydraulic cylinder) through a hydraulic main line by means of a hydraulic pump placed in the hydraulic main line in order to actuate the hydraulic unit with the oil, and a wind turbine generator provided therewith.
2. Description of the Related Art
FIG. 6 shows the outline of a hydraulic (actuation) system of a hydraulic unit for wind turbine blade pitch actuation, in which the hydraulic unit for blade pitch actuation designated by reference numeral 1 is supplied with oil 15 stored in a hydraulic tank 14 through a hydraulic main line 8.
A hydraulic pump 4 to be driven by a motor 5 is placed in the hydraulic main line 8, and the oil 15 in the hydraulic tank 14 is fed by the hydraulic pump 4 into the hydraulic unit 1 through the hydraulic main line 8. A check valve 16 capable of feeding oil only on the side of the hydraulic unit 1 is provided in the hydraulic main line 8.
In such a hydraulic system for blade pitch actuation, if the hydraulic pump of the hydraulic system is used in cold climates reaching about −30 degrees C., the oil temperature has to rise to −10 degrees C. or more to prevent damage to the equipment.
To this end, a heater 30 is placed to warm the oil 15 stored in the hydraulic tank 14. The temperature of the oil 15 in the hydraulic tank 14 is detected by a temperature sensor 7.
However, the method using such a conventional heater 30 takes three to four hours to rise the oil temperature from −30 degrees C. to −10 degrees C. at startup, for example, thus requiring a lot of time and the installation cost of the heater 30.
Patent Document 1 (Japanese Examined Utility Model Application Publication No. 61-23520) shows a hydraulic system adapted to open a logic valve (bypassed state) upon startup of a hydraulic pump in a hydraulic system for a steering gear and close the logic valve when the hydraulic pump reaches the steady rotation.
Further, in the hydraulic system for wind turbine blade pitch actuation as shown in FIG. 6, if some load is left in the hydraulic system when the hydraulic system (hydraulic pump) is actuated at startup, excess current T flows through a motor 5 suddenly for a short time as shown in FIG. 7 to increase the load on the hydraulic system (hydraulic pump), resulting in an overload. If this overloaded state at startup is repeated, a problem can occur with wind turbine blade pitch or blade control.